Error recovery and power management between nodes of an interconnection network

ABSTRACT

Improved techniques for recovering from an error condition without requiring a re-transmittal of data across a high-speed data link and for improved power usage are disclosed herein. A data stream is initiated. This stream includes different types of packets. Error correcting code (ECC) is selectively imposed on a control data type packet. A transmitter node and a receiver node are connected via a hard link that has multiple virtual channels. Each virtual channel is associated with a corresponding power-consuming node. When the receiver node receives the control data type packet, error correction is performed if needed without re-transmittal. When a final data type packet is transmitted for each virtual channel, the transmitter node transmits an end condition type packet. A corresponding power-consuming node that corresponds to the respective virtual channel transitions from an active state to a low power state.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/345,910 filed on Jun. 11, 2021, entitled “ERROR RECOVERY AND POWERMANAGEMENT BETWEEN NODES OF AN INTERCONNECTION NETWORK,” which is acontinuation of U.S. patent application Ser. No. 16/880,018 filed on May21, 2020, entitled “ERROR RECOVERY AND POWER MANAGEMENT BETWEEN NODES OFAN INTERCONNECTION NETWORK,” which issued as U.S. Pat. No. 11,050,514 onJun. 9, 2021, which applications are expressly incorporated herein byreference in their entirety.

BACKGROUND

A computing architecture may comprise any number of interconnectednodes, such as CPUs, GPUs, NICs, Wi-Fi cards, memory, and so forth.These various nodes can be connected to one another via different typesof connections, including wired connections or even wirelessconnections.

A wired connection is often referred to as a “hard link” and physicallyconnects one node to another node. One type of wired connection (andspecifically a type of bus protocol) is the PCIe (peripheral componentinterconnect express) connection. PCIe is a type of interface designedto connect high-speed nodes together. PCIe links come in numerousdifferent configurations and may include differing numbers of “lanes” or“channels” which are paths through which data is permitted to travelfrom one node to another node. By way of example, PCIe links often havebetween 1 and 32 different lanes. FIG. 1 illustrates an exampleconnection terminal 100, which may be any type of high-speed connectionterminal, including PCIe. This connection terminal 100 is shown asincluding at least one channel 105 (aka a lane) as well as a number ofpackets (e.g., packet 110 and packet 115) traversing that channel 105.In this example illustration, the packets 110 and 115 are represented asvehicles to help with the following analogous description. The packets110 and 115 travel the channel 105 in accordance with the bus protocol120 the connection terminal 100 uses (e.g., the bus protocol 120 may bethe PCIe protocol, or some other high-speed protocol).

In this example, the channel 105 can be thought of as a one-lane road onwhich cars (e.g., the packets 110 and 115) travel. With a one lane road,each subsequent car is limited by the speed of a preceding car. Forinstance, if the packet 110 were delayed for some reason on the channel105, then the packet 115 will also be delayed. Increasing the number ofchannels allows for more data packets to be transmitted from one node toanother node. For instance, if the connection terminal 100 were toinclude a second channel, then data packets could move across those twochannels at two packets per cycle, and so on based on the number ofchannels.

With that basic understanding, it should now be noted how each channel(e.g., channel 105) typically has its own corresponding buffer. Thereason packet 115 is not able to “pass” packet 110 is because packet 110is currently allocated to the channel 105's buffer. Packet 115 is unableto use the buffer until such time as packet 110 is released from thebuffer. Therefore, if packet 110 is blocked or remains idle while beingallocated to the buffer, the subsequent packets will also remain idle.Increasing the number of channels in the hard link enables more data tobe transmitted by enabling parallel transmittal, but hard links areoften limited in physical size, thereby restricting the number ofchannels.

The concept of virtualization has been introduced to solve some of thesizing constraints associated with hard links. A so-called “virtual”channel operates by decoupling resources (e.g., a buffer) that werepreviously allocated to the actual channel. This decoupling is performedby effectively providing multiple different buffers for each singlechannel. FIG. 1B is illustrative.

FIG. 1B shows a connection terminal 125, which is representative of theconnection terminal 100, and a channel 130, which is representative ofthe channel 105. Here, channel 130 has had its buffer resourcesvirtualized to effectively sub-divide the channel into multiple channelsor lanes. For instance, channel 130 is shown as including a virtual lane135 and a virtual lane 140. Additionally, a set of packets are beingtransmitted across lane 135 (e.g., see packet 145) and a different setof packets are being transmitted across lane 140 (e.g., see packet 150).Now, the channel 130 is able to support a larger number of packets thanchannel 105, and the packets travelling along that channel may not beimpeded by an idling packet in a different lane. In this regard, the“road” of channel 130 has been modified to include additional lanes,similar to a multi-lane highway. Further, if packet 145 were blocked, adifferent buffer is available to enable packet 150 to be transmitted.Accordingly, implementing virtual channels in a hard link is similar tothe idea of adding new lanes to a road system.

When it comes to hard links, the resource that is considered to be themost costly is typically the bandwidth of the hard physicalwire/channel. Buffer memory is often viewed as being the second mostcostly resource. Virtualization of the hard link achieves significantefficiency gains because those resources are used in a more efficientmanner via the decoupling mentioned earlier. While virtualization doesadd a small expense, its expense is overshadowed by the other efficiencygains.

While high-speed connection terminals and protocols (e.g., PCIe) providesubstantial benefits, these types of terminals can require high levelsof power to operate. When these types of terminals are used inbattery-powered computing architectures, the higher power drains canimpose substantial burdens on the system.

Additionally, as is usually the case with many computing components,errors can occur when data packets are being transmitted. For instance,transient errors may occur from any number of factors, includingenvironmental factors (e.g., temperature, electrostatic buildup,humidity, etc.), rough handling of the system, and so forth. Traditionalbuses handle these errors in an unsophisticated manner by simplyre-transmitting the data when an error is detected. Some systems,however, have a real-time need (or a need that approximates real-time)for the data, so re-transmittal may not be a viable solution.Accordingly, although traditional systems provide many benefits, thesesystems are still quite inadequate when design considerations requirelow power and real-time usage of transmitted data.

The subject matter claimed herein is not limited to embodiments thatsolve any disadvantages or that operate only in environments such asthose described above. Rather, this background is only provided toillustrate one exemplary technology area where some embodimentsdescribed herein may be practiced.

BRIEF SUMMARY

Embodiments disclosed herein relate to systems, devices (e.g., hardwarestorage devices, wearable devices, etc.), and methods configured toimprove transmissions between a transmitter node and a receiver node viaa high-speed high-bandwidth link by recovering from an error conditionwithout requiring a re-transmittal of data.

In some embodiments, a data stream is initiated, where this data streamis designed to include packets of different data types, including acontrol data type and a non-control data type. A control data typepacket is generated. Here, error correcting code (ECC) is selectivelyimposed on the control data type packet. This ECC is configured toenable errors occurring in the control data type packet to be correctedat the receiver node. Consequently, re-transmittal of the control datatype packet is prevented. The transmitter node then transmits thecontrol data type packet to the receiver node. Upon receipt of thecontrol data type packet at the receiver node, error correction on thecontrol data type packet using the ECC is performed when an error isdetected or, alternatively, error correction is refrained from beingperformed when no error is detected. Additionally, non-control data typepackets are generated. Here, the embodiments selectively refrain fromimposing the ECC on the non-control data type packets. The process ofselectively refraining from imposing the ECC on the non-control datatype packets operates to reduce bandwidth usage over the hard link ascompared to imposing ECC on the non-control data type packets. Thetransmitter node then begins transmitting the non-control data typepackets to the receiver node. Upon receipt of the non-control data typepackets at the receiver node and in response to an error in anon-control data type packet being detected, the embodiments allowcorruption of data in the non-control data type packet to persistbecause this corruption is negligible.

Some embodiments are configured to improve power usage of a device(e.g., a battery operated device) by identifying when packettransmissions across virtual channels are complete and by causing nodesto enter a low power state/mode when those packet transmissions arecomplete.

Here, a transmitter node and a receiver node are connected via a hardlink. Additionally, multiple virtual channels are initialized on thehard link, where each virtual channel is associated with a correspondingpower-consuming node. Data streams are generated, where these streamsare configured to include packets of different types, including a datatype packet and an end condition type packet. The embodiments generatethe packets and cause the transmitter node to transmit the packets tothe receiver node over the virtual channels. Each virtual channeltransmits one or more of the packets in different data streams. For eachrespective virtual channel, a number of operations are performed. Oneoperation includes identifying when a final data type packet has beentransmitted across each respective virtual channel. Another operationincludes causing the transmitter node to transmit (for that respectivevirtual channel) one or more end condition type packets. Anotheroperation includes causing a corresponding power-consuming node thatcorresponds to the respective virtual channel to transition from anactive state to a low power state/mode. After final data type packetshave been transmitted across all of the virtual channels, thetransmitter node also sends a final end condition type packet to thereceiver node. This final end condition type packet informs the receivernode that the data stream is complete.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

Additional features and advantages will be set forth in the descriptionwhich follows, and in part will be obvious from the description, or maybe learned by the practice of the teachings herein. Features andadvantages of the invention may be realized and obtained by means of theinstruments and combinations particularly pointed out in the appendedclaims. Features of the present invention will become more fullyapparent from the following description and appended claims or may belearned by the practice of the invention as set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features can be obtained, a more particular descriptionof the subject matter briefly described above will be rendered byreference to specific embodiments which are illustrated in the appendeddrawings. Understanding that these drawings depict only typicalembodiments and are not therefore to be considered to be limiting inscope, embodiments will be described and explained with additionalspecificity and detail through the use of the accompanying drawings inwhich:

FIGS. 1A and 1B provide an introduction to virtualizing hard links.

FIG. 2 illustrates how data packets are able to travel over virtualchannels from one node to another node.

FIG. 3 illustrates an example head-mounted device (HMD) that may requirelow power usage for hard links and real-time data usage requirements.

FIG. 4 illustrates some internal features, including a high-speed link,of the HMD.

FIG. 5 illustrates an abstracted viewpoint of some of the computingcomponents of the HMD.

FIG. 6 illustrates how an HMD can use a laser-basedmicroelectromechanical scanning (MEMS) mirror system to display content.

FIGS. 7A, 7B, and 7C illustrate additional features regarding the MEMSmirror system.

FIG. 8 illustrates some operational requirements that are considered bythe disclosed embodiments.

FIG. 9 illustrates the use of different types of packets fortransmitting data to achieve the benefits disclosed herein.

FIG. 10 illustrates how error correcting code (ECC) may be used to helpprevent re-transmittal of data.

FIG. 11 illustrates how the different packet types can be transmittedover any number of virtual channels or virtual lanes.

FIG. 12 illustrates a power saving technique that operates to transitionnodes to a low power state when certain packets are detected.

FIG. 13 illustrates how errors can be mitigated when attempting toidentify the end of a data stream, where those errors are mitigated viathe use of a specially configured end condition type packet. Multipleend condition type packets may be transmitted to reduce the likelihoodof misidentifying the end of a data stream.

FIG. 14 illustrates an example of a data stream that includes thedifferent types of packets.

FIG. 15 illustrates how a receiver node can be configured to include adeadman timer.

FIG. 16 illustrates a flowchart of an example method for improvingtransmissions between a transmitter node and a receiver node via ahigh-speed high-bandwidth link by recovering from an error conditionwithout requiring a re-transmittal of data.

FIG. 17 illustrates a flowchart of an example method for improving powerusage by identifying when packet transmissions across virtual channelsare complete and by causing nodes to enter a low power state when thosepacket transmissions are complete.

FIG. 18 illustrates an example computer system configured to be able toperform any of the disclosed operations.

DETAILED DESCRIPTION

Embodiments disclosed herein relate to systems, devices (e.g., hardwarestorage devices, wearable devices, etc.), and methods configured toimprove transmissions between a transmitter node and a receiver node viaa high-speed high-bandwidth link (e.g., the link has 4×-8× the bandwidthrequirements of standard PCIe) by recovering from an error conditionwithout requiring a re-transmittal of data.

In some embodiments, a data stream is initiated. This stream includes acontrol data type packet and a non-control data type packet. Errorcorrecting code (ECC) is selectively imposed on the control data typepacket. This ECC enables errors occurring in the control data typepacket to be corrected at the receiver node. When the receiver nodereceives the control data type packet, error correction is performed ifneeded. The embodiments also selectively refrain from imposing ECC onthe non-control data type packets. When the receiver node receives thenon-control data packets and in response to an error in the non-controldata type packets being detected, the embodiments allow the corruptionof this data to persist because it has an acceptable level of impact.

Some embodiments are configured to improve power usage of abattery-operated device by identifying when packet transmissions acrossvirtual channels are complete and by causing nodes to enter a low powerstate when those packet transmissions are complete.

In some embodiments, a transmitter node and a receiver node areconnected via a hard link that has multiple virtual channels initializedthereon. Each virtual channel is associated with a correspondingpower-consuming node. Data streams are generated, where these streamsinclude data type packets and end condition type packets. Thetransmitter node transmits the packets to the receiver node over thevirtual channels. Each virtual channel transmits one or more of thepackets. For each respective virtual channel, a number of operations areperformed. One operation includes identifying when a final data typepacket has been transmitted across each respective virtual channel.Another operation includes causing the transmitter node to transmit (forthat respective virtual channel) an end condition type packet. Anotheroperation includes causing a corresponding power-consuming node thatcorresponds to the respective virtual channel to transition from anactive state to a low power state. After final data type packets havebeen transmitted across all of the virtual channels, the transmitternode sends a final end condition type packet to the receiver node. Thisfinal end condition type packet informs the receiver node that all ofthe data streams across all of the virtual channels are complete.

Examples of Technical Benefits, Improvements, And Practical Applications

The following section outlines some example improvements and practicalapplications provided by the disclosed embodiments. It will beappreciated, however, that these are just examples only and that theembodiments are not limited to only these improvements.

The disclosed embodiments improve the existing technology in numerousways. For instance, by practicing the principles disclosed herein, theembodiments are able to reduce the amount of bandwidth consumed bypackets transmitted over virtual channels when errors are detected forthose packets. That is, whereas previous systems simply re-transmittedfaulty or error-ridden packets (thereby consuming additional bandwidthover the virtual channel), the embodiments are able to selectively applyerror correcting code (ECC) to certain types of high priority “control”data type packets. These types of packets are packets that includecontrol information regarding how a set of subsequent packets (i.e.non-control data type packets) are to be utilized.

The control data type packets are differentially compressed and operateto control how the data in the non-control data type packets is used.Whereas an error on a single non-control data type packet results in anacceptable level of corruption, an error to the control data typepackets may potentially result in corruption for the entire remainingdata stream. As such, the embodiments beneficially apply ECC to thecontrol data type packets. Because each data stream typically includesonly a single control data type packet, imposing the ECC results in anominal increase to the virtual channel's bandwidth. Despite thisnominal increase, the benefits that are achieved by the ECC aresubstantial because the ECC allows for the receiving node to correctand/or detect the errors without requiring re-transmittal of the controldata type packet (i.e. the system is resilient to errors without are-transmit). As such, the embodiments improve the operationalefficiency of the computer system by eliminating or at least reducingthe likelihood of requiring packet re-transmittal. Additionally, ECC isnot traditionally used for bus protocols; instead, ECC is typically usedfor memory-based operations. In this regard, the embodiments are alsoutilizing ECC in a new manner.

The disclosed embodiments also improve the technical field by minimizingor reducing the amount of battery consumption that is consumed.Specifically, the embodiments configure and utilize a so-called “endcondition packet” or “end condition type packet” that is speciallyconfigured to impose nominal usage of the virtual channel's bandwidthwhile also acting as a flag to trigger a power-consuming node totransition to a low power state/mode. Because each virtual channel maybe associated with its own corresponding power-consuming node, the endcondition packets, which may be sent across the different virtualchannels at different times, enables the system to reduce power usage byallowing nodes to turn off at earlier times as compared to conventionalsystems. In this regard, the embodiments improve the battery usage ofthe computer system by enabling power-consuming nodes to transition tolow power states/modes earlier than what was previously available inconventional systems. In actual implementations, the embodiments haveachieved upwards of 8× the power savings of conventional systems.

In embodiments dealing with a scanning MEMS mirror, the system is alsoable to beneficially supply all the lasers with a minimum virtualchannel buffer at roughly the same time. So the length of the data thatis sent per virtual stream is relatively low (single % of the line ofpixels or sweep). The hardware is able to keep each virtual channelsupplied with data so the data can be given to the lasers with a verylow latency while not consuming a large amount of the buffer'sbandwidth. Some of these features may also be implemented by hardwaresuch that the software stack is essentially non-existent.

Additionally, the embodiments are able to beneficially capitalize onvirtualization. For instance, suppose an error occurs on one of thevirtual channels. The embodiments are able to allow the other virtualchannels to complete their transmissions and processes despite the onevirtual channel experiencing an error. By way of a specific example,suppose a red laser corresponds to one virtual channel. Further supposean error occurs relative to this virtual channel. The other lasers andthe other virtual channels are able to complete their respectiveoperations despite the error occurring on the one virtual channel. Bytransmitting the end condition packet, the system is also able to resetitself (e.g., the laser and virtual channel that experienced the error)despite the error so that the laser and virtual channel can still beused.

Interconnection Networks

Attention will now be directed to FIG. 2 , which illustrates an exampleof an interconnection network 200. The interconnection network 200 maycomprise any number of interconnected nodes, such as node 205 and node210. Examples of nodes 205 and 210 may be any type of computingcomponent, including high-speed computing components. For instance, thenodes 205 and 210 can be any type of CPU, GPU, HPU (holographicprocessing unit), DMA (display module assembly) chip, a MEMS system,memory, and so forth, without limit. As shown, node 205 is connected ortethered to node 210 via a high-speed link 215. High-speed link 215 maybe any type of physical channel connection that supports high-speed datatransmissions.

Communication between node 205 and node 210 occurs by transmittingmessages from a transmitter node (e.g., node 205) to a receiver node(e.g., node 210) (though the messages can potentially be transmittedback and forth). A message may be divided or broken down into one ormore different “packets” that are transmitted in the form of a datastream 220. As used herein, a “packet” is the smallest body or unit ofdata/information that contains routing, sequencing, and payloadinformation. That is, the message may be subdivided into any number ofconstituent parts, and those parts may be transmitted in the form of apacket, such as packets 225, 230, and 235. In the example of FIG. 2 ,the node 205 is a transmitter node because node 205 is sending the datastream 220 to the node 210, which is a receiver node. When the node 210receives the packets, the node 210 will organize the packets to reformthe original message.

Embodiments disclosed herein may virtualize the high-speed link 215 toinclude any number of virtual channels. For instance, the hard link 240is representative of the high-speed link 215. This hard link 240 isshown as including any number of virtual channels, such as virtualchannels 245, 250, 255, and 260. Packets (e.g., packet 265) are shows asbeing transmitted across those different virtual channels.

Each virtual channel is associated with its own respective buffer. Forinstance, virtual channel 245 may be associated with buffer 270, andvirtual channel 250 may be associated with buffer 275. The other virtualchannels are associated with their own respective buffers, even thoughthat is not currently shown in FIG. 2 . Each buffer may have acorresponding buffer size 280. In accordance with the disclosedprinciples, hardware is able to keep the channel's bandwidth balancedbetween various requesters (i.e. receiving nodes). In some cases, thebuffer sizes for all of the different buffers may be the same while inother cases the buffer sizes may be different. Some buffer sizes may bethe same for some buffers while other buffer sizes may be different. Inany event, the buffer size 280 is based on the total buffer sizeavailable for the hard link 240. In some cases, the length of dataincluded in any particular packet of the data stream is restricted basedon buffer sizes of virtual channels initialized for the hard link.Accordingly, FIG. 2 shows how packets may be transmitted from one nodeto another node via a high-speed link.

Example Head-Mounted Device (HMD)

Attention will now be directed to FIGS. 3, 4, and 5 . These figuresprovide example illustrations of a head-mounted device (HMD), which is acomputing architecture that may include any number of interconnectednodes or the interconnection network 200 of FIG. 2 . Notably, while asubstantial portion of this disclosure is focused on the use of nodes inan HMD, one will appreciate that the disclosed principles are notlimited to only these scenarios. Rather, nodes can be included in anytype of computing architecture, without restriction, and the embodimentsmay be practiced with those different computing architectures.Accordingly, the discussion surrounding the HMD is for example purposesonly and should not be interpreted as being limiting.

Mixed-reality (MR) systems, including virtual-reality (VR) andaugmented-reality (AR) systems, have received significant attentionbecause of their ability to create truly unique experiences for theirusers. For reference, conventional VR systems create completelyimmersive experiences by restricting their users' views to only virtualenvironments. This is often achieved through the use of a head-mounteddevice (HMD) that completely blocks any view of the real world. As aresult, a user is entirely immersed within the virtual environment. Incontrast, conventional AR systems create an augmented-reality experienceby visually presenting virtual objects that are placed in or thatinteract with the real world.

As used herein, VR and AR systems are described and referencedinterchangeably. Unless stated otherwise, the descriptions herein applyequally to all types of MR systems, which (as detailed above) include ARsystems, VR reality systems, and/or any other similar system capable ofdisplaying virtual content.

FIG. 3 shows a user 300 wearing an HMD 305A, which is an example of theMR system mentioned above. The user 300 can wear the HMD 305A to viewand interact with an MR scene. HMD 305B, which is a blown-up view of theHMD 305A, includes a display 310, a first arm 315, and a second arm 320.As shown, the display 310 is oriented towards the front of the HMD 305Bso as to be positioned near the user's eyes.

It will be appreciated that display 310 can include any type of display.In some embodiments, display 310 includes a microelectromechanicalscanning (MEMS) mirror display in which image pixels are individuallyrastered by a laser and mirror assembly. In other embodiments, display310 includes any type of light-emitting diodes, plasma displays, liquidcrystal displays, and so on. Accordingly, any type of display may beincluded within HMD 305B, and the embodiments should not be limited to aparticular type.

FIG. 4 shows an HMD 400, which is an abstracted representation of theHMD 305B from FIG. 3 , using some abstracted block depictions torepresent HMD components. It will be appreciated that these blocks arefor example purposes only and should not be viewed literally as havingblock-like shapes.

HMD 400 includes a first adjustable flex-fit arm 405 (i.e. the same asin FIG. 3 ) and a second adjustable flex-fit arm 410. The firstadjustable flex fit arm 405 is shown as including any number oflow-speed links 405A (aka wires or channels) while the second adjustableflex fit arm 410 is shown as including any number of high-speed links410A. Of course, the high-speed and low-speed wires can be positioned oneither side of the HMD and are not limited to a specific side. Furtherdetail on these wires will be provided later. Furthermore, it should benoted that these wires may be configured as ribbons and/or bundledcables.

The high-speed links 410A can be used to transmit high-speed displaydata and/or sensor data (e.g., camera data, such as head tracking anddepth detection) between the compute units located in the front-endhousing and the compute units located in the back-end housing. Thesehigh-speed links 410A are designed to have low latency, thereby enablinga high number of compute cycles or communications to be passedtherethrough.

In contrast, the low-speed links 405A can be used to provide power,ground (e.g., connections to a battery), or switching mechanisms. Thatis, in some cases, the low-speed links 405A also include switches orsignals that can operate at lower speeds as compared to the computecycles of the high-speed links 410A.

HMD 400 also includes a front-end housing 415, which includes a firstcompute unit 420 and wiring 425. The ellipsis 430 is provided toillustrate how the front-end housing 415 may include additionalcomponents or structures as well.

The first compute unit 420 is shown as including a number of differentcompute elements. Specifically, these compute elements include, but arenot limited to, display circuitry 420A (e.g., such as display 310 fromFIG. 3 , including a digital display processing (DPP) chip, an analogchip that drives a display module assembly (DMA), the DMA itself,lasers, and a MEMS mirror system), one or more CPU(s) 420B (i.e. centralprocessing units), one or more GPU(s) 420C (i.e. graphical processingunits), and a SOC 420D (i.e. a system on chip). These computeelements/units are provided to render any number of virtual images for auser to view and interact with.

HMD 400 also includes a back-end housing 435, which includes a secondcompute unit 440, a battery 445, and wiring 450. The ellipsis 455demonstrates how any number of other compute elements, structures, orfeatures may be included with the back-end housing 435. The firstadjustable flex fit arm 405 connects the front-end housing 415 to theback-end housing 435, and the second adjustable flex fit arm 410similarly connects the front-end housing 415 to the back-end housing435.

The second compute unit 440 is shown as including one or more CPU(s)440A, one or more GPU(s) 440B, and a holographic processing unit HPU440C. As used herein, an HPU (e.g., HPU 440C) refers to a computeprocessing unit that obtains and integrates real-world data into an MRscene. In some cases, HPU 440C controls any number of inertialmeasurement units (IMU), head and hand tracking cameras, and depthcameras to generate a spatial mapping of the real-world environment.Using this spatial mapping, HMD 400 (and in particular HPU 440C) cancause holograms or virtual images to be projected for the user to viewand interact with.

It will be appreciated that although SOC 420D is shown as being includedin the front-end housing 415 and the HPU 440C is shown as being includedin the back-end housing 435, the positions can be reversed. In othercases, both of the compute units can be included in the front-endhousing 415 or both can be included in the back-end housing 435.Accordingly, FIG. 4 is provided to simply show one exampleimplementation regarding the placement and configuration of some of thecompute units of an HMD. Additionally, the battery 445 can also bepositioned in the front-end housing 415 if so desired.

FIG. 5 provides another perspective of an HMD 500, which isrepresentative of the HMDs discussed thus far. HMD 500 includes afront-end housing 505, just like front-end housing 415 of FIG. 4 . HMD500 also includes arm 505, with a bundled cable 510 passingtherethrough. At a different segment of arm 505, the electrical wiresare bundled together at the bundling portion 515 where they arestructured as a nested cable ribbon 520.

HMD 500 includes another arm 525, with a bundled cable 530 passingtherethrough. Similarly, arm 525 also includes a nested cable ribbon535. Accordingly, the HMD 500 includes two arms (e.g., arm 505 and arm525), with each arm having a corresponding set of electrical wirespassing through the internal confines, or rather the internal cavities,of those arms.

The high-speed link 215 from FIG. 2 may be representative of thehigh-speed links 410A from FIG. 4 . Similarly, the ribbon 520 and thebundled cable 510 from FIG. 5 may be representative of the high-speedlink 215. The nodes 205 and 210 from FIG. 2 may be representative of anyof the compute units illustrated in FIG. 4 , such as the displaycircuitry 420A, the CPU(s) 420B and 440A, the GPU(s) 420C and 4406, theSOC 420D, and the HPU 440C. In some embodiments, the nodes may beindividual compute units located within either one of the front-endhousing 415 of FIG. 4 or the back-end housing 435. For instance, thedisplay circuitry 420A may include any number of lasers, digital displayprocessing (DPP) chips, DMAs, DMA-driving chips, or MEMS mirror systems.These compute units may also be representative of the nodes introducedin FIG. 2 .

Additionally, these compute units may have shortened high-speed linksconnecting those elements. To clarify, whereas the high-speed links 410Ashown in FIG. 4 illustrate how the front-end housing 415 can beconnected to the back-end housing 435, it may be the case that there areadditional high-speed links connecting individual nodes located withinthe front-end housing 415 exclusively or within the back-end housing 435exclusively. In that case, those links will be relatively shorter thanthe high-speed links 410A. In any event, the HMDs discussed herein mayuse any number of high-speed links to connect different high-speedcompute units, such as those described above.

Laser-Based MEMS Display System

FIG. 6 shows some components that may be included within a display for aMR computing system, which includes HMD 600. HMD 600 is representativeof the HMDs discussed thus far. The illustrated components arebeneficially provided to render any type of virtual image. Specifically,FIG. 6 focuses on the display circuitry 605 used to render images, whichcircuitry is representative of the display circuitry 420A of FIG. 4 .The display circuitry 605 includes, but is not limited to, a digitaldisplay processing (DPP) chip 610, an analog display module assembly(DMA) driving chip 615, the DMA 620, laser emitters 625 and 630 (thoughmore or less may be provided), and a MEMS system 635. A DMA is oftenarchitected for up to four different lasers, so it may be the case thatthere are multiple DMAs in the HMD 600.

In practice, the DPP chip 610 transmits image data (in the form ofpackets) to the DMA-driving chip 615 over a high-speed high-bandwidthhard link at a rate so that the line of data being transmitted istypically one “sweep” ahead of where certain lasers are actuallyprojecting data. Consequently, the buffers of the virtual lanes arebeing used to pre-send pixel information for pixels that are to beilluminated at some point in the future. Further details on “sweeps”will be provided later.

In this regard, the laser emitters 625 and 630 function as projectorsfor the HMD 600. The virtual channels are able to buffer theone-sweep-ahead display data in the packets. The DPP chip 610, theDMA-driving chip 615, the laser emitter 625, and even the MEMS system635 may all be considered “nodes,” as referred to in the earlierfigures. Furthermore, there is a high-speed link 640 between at leastthe DPP chip 610 and the DMA-driving chip 615. Other high-speed linksmay be present between any of the other nodes as well. The DPP chip 610operates to provide information regarding how images are to be projectedvia the MEMS system 635.

Laser emitter 625 (aka “laser assembly,” “laser device,” or simply“laser”) includes one or more lasers. The example shown in FIG. 6illustrates a (first) laser 625A, a (second) laser 625B, and a (third)laser 625C, though more or less may be provided. Examples of theselasers may be a red laser, a green laser, and a blue laser such that thelaser emitter 625 is a red, green, blue (RGB) laser assembly having RGBlasers. While only three lasers are presently shown, it will beappreciated that any number of lasers may be provided in HMD 600 (e.g.,perhaps 1-4 red lasers, 1-4 green lasers, and 1-4 blue lasers).Moreover, in some embodiments, lasers 625A, 625B, and 625C may beincluded within their own different discrete packaging unit. In someembodiments, an infrared (IR) laser may be included as a part of laseremitter 625 or within a separate packaging unit.

In some embodiments, such as the one shown in FIG. 6 , the laser lightfrom the lasers 625A, 625B, and 625C is optically/spectrally combined toform RGB laser light 640. That is, the laser light 640A from laser 625A,the laser light 640B from laser 625B, and the laser light 640C fromlaser 625C is optically/spectrally combined (e.g., either within thelaser emitter 625 or outside of the laser emitter 625) to produce asingle collimated beam of red, green, and blue RGB laser light 640. Itwill be appreciated that RGB laser light 640 may be a continuous beam ofRGB laser light, or, alternatively, it may be a pulsed beam of RGB laserlight.

RGB laser light 640 is then directed to a microelectromechanicalscanning (“MEMS”) mirror system 635. MEMS mirror system 635 includes amulti-directional mirror array that is able to rapidly redirect and aimlaser light to any desired pixel location. For example, scanningdirection 645 shows how MEMS mirror system 635 is able to rapidlyredirect pulsed or continuous scanning laser light 650 and scanninglaser light 655 to any location. Here, scanning laser light 650 and 655originate from RGB laser light 640.

While only two instances of the scanning laser light are labeled, itwill be appreciated that MEMS mirror system 635 is able to redirect anynumber of laser emissions. By scanning laser light back and forthhorizontally and up and down vertically, the display circuitry 605 isable to illuminate individual pixels of a virtual image within a desiredfield of view. Because the display circuitry 605 is able to illuminateindividual pixels so rapidly, display circuitry 605 is able to render anentire virtual image (e.g., an image frame) for a user to view andinteract with without the user realizing that the virtual image wasprogressively generated by scanning individual pixels.

In some embodiments, the display circuitry 605 includes more than onelaser emitter. For instance, FIG. 6 shows a (second) laser emitter 630.In cases where there are more than one laser emitter, then the emitterscan be configured to jointly or concurrently illuminate pixels togenerate an image frame. In some cases, the different laser emitters maybe associated with different DMAs as well. In some embodiments, an imageframe is illuminated by one, two, or more than two separate laseremitters. In some implementations, there may be 12 different lasers, oreven more than 12 lasers. In some cases, the multiple separate laseremitters concurrently illuminate corresponding pixels. In other cases,the multiple separate laser emitters stagger when pixels areilluminated.

FIGS. 7A, 7B, and 7C further expand on the operations of a MEMS mirrorsystem by showing how a MEMS/laser unit 700A can be used in a VR type ofHMD and how a MEMS/laser unit 700B can be used in an AR type of HMD,respectively. MEMS/laser units 700A and 700B are both exampleimplementations of the MEMS mirror system 635 shown in FIG. 6 . Pulsedor continuous laser light 650 and laser light 655 in FIG. 6 are exampleimplementations of laser light 705A and 705B.

In FIG. 7A, the display 710 is representative of a VR display of a VRtype HMD. As described earlier, in a VR situation, the user's view ofthe real-world is entirely occluded such that the user is able to seeonly a VR environment. Here, display 710 is shown as including avertical field of view (“FOV”) and a horizontal FOV. FIG. 7A also showsthe progressively backward and forward horizontal and upward anddownward vertical scanning direction 715 in which the MEMS/laser unit700A is able to scan individual pixels of a virtual image onto thedisplay 710. By rapidly scanning/rastering the individual pixels, theMEMS/laser unit 700A is able to render an entire virtual image or evenan entire VR environment.

Building on the earlier discussion, it will be appreciated that eachpixel rastered on the display 710 is generated by pulsing the laserincluded within the MEMS/laser unit 700A. In this manner, it is possibleto illuminate each pixel on display 710 in a pixel-by-pixel basis allthe way from the top portion of the display 710 to the bottom portion ofthe display 710. Consequently, as the MEMS mirror system in theMEMS/laser unit 700A is scanned/aimed at a given pixel position on thedisplay 710, the laser is pulsed to a determined intensity or poweroutput level so as to properly illuminate that pixel within the overallvirtual image. The frame is over when the last pixel is illuminated, andthe MEMS/laser unit 700A enters a so-called “vblank” time period inwhich the MEMS/laser unit 700A resets its mirrors to an originalstarting position so as to generate a new frame. The period of time toscan each new frame and to reset during the vblank period is referred toas the refresh rate 720. Examples rates for the refresh rate 720 can bebetween 90 Hz and 120 Hz, though other rates may be used as well.

FIG. 7B shows an example implementation within an AR system. Instead ofscanning pixels on a display (e.g., display 710), the AR system causesits MEMS/laser unit 700B to scan pixels onto the user's eye through theuse of a waveguide 725, which receives the laser light and then directsthe laser light towards the user's eye. In this regard, FIG. 7B isrepresentative of a scanning waveguide display.

To illustrate, FIG. 7B shows MEMS/laser unit 700B generating pulsedlaser light 705B which is directed towards waveguide 725. Waveguide 725includes an entry grating 730 (aka an “input port” or “input grating”),through which pulsed laser light 705B enters waveguide 725, and an exitgrating 735, through which pulsed laser light 705B exits waveguide 725.Waveguide 725 is structured to enable the pulsed laser light 705B topropagate through it so that the pulsed laser light 705B can beredirected to a desired location, such as the scanning area 740. In manyinstances, the scanning area 740 corresponds to a user's eye.

FIG. 7C illustrates the vblank time 745 and a sweep 750. As describedearlier, the vblank time 745 is the period of time in which no pixelsare being illuminated (thus no data stream is being transmitted betweenthe DPP chip 610 and the DMA-driving chip 615); rather, the MEMS systemis resetting its mirror to return to an original start position so as tobegin generating a new frame. Often, the vblank time 745 consumesbetween 10%-30% of the frame's time period. In some cases, the vblank745 is about 20% of the time allocated for the particular frame. Thesweep 750 refers to a single horizontal pass of the MEMS mirror systemwhen scanning an individual line of pixels of the frame. Stateddifferently, a sweep is half of a full period of the fast scan mirror ofthe MEMS mirror system. By way of example and not limitation, the sweep750 can be considered or viewed as a line of pixels spanning from oneside of the display (or scanning area) to the other side of the display(or scanning area).

Notably, it may be the case that not every pixel of a sweep will beilluminated by all the lasers (also it may be the case that each virtualchannel corresponds to a respective laser). Consequently, it may be thecase that there are different sweep sizes per virtual channel.

Accordingly, the disclosed principles may be practiced in any type ofcomputing architecture. In some implementations, the principles areutilized in the context of an HMD and in particular for some of thedifferent nodes of the HMD (e.g., the DPP chip 610 and the DMA-drivingchip 615 of FIG. 6 ). Additional details regarding the variousoperations of the embodiments will now be discussed in more detail inthe following sections.

Improved Techniques for Power Usage And Error Correction/Detection

Attention will now be directed to FIG. 8 , which lists a number ofoperational requirements 800, or rather, operational features, that maybe followed by one, some, or all of the disclosed embodiments. Theserequirements will be introduced at a high level at this point, and afurther discussion regarding these requirements will be provided laterthroughout the remaining portion of this disclosure.

Initially, the operational requirements 800 include a real-time datarequirement 805. As discussed earlier in connection with the HMDs, theHMDs are used to display content to a user. The HMD has the real-timerequirement 805 because it needs to draw something on its screen (orotherwise illuminate pixels), and the data pipeline for instructing howto draw those pixels is already working on new pixels to draw (e.g., theone sweep ahead aspect mentioned earlier), so it is desirable to avoidre-transmitting data. To further clarify, each laser of the HMD may haveits own real-time requirements for when pixel data is to be received bythe chip(s) driving those lasers.

Furthermore, the content dynamically changes based on a number ofdifferent factors, some of which include pose/orientation of the HMD,scene changes of the MR scene, interactions with the holograms, and soforth. As such, when the embodiments are practiced in the context of anHMD, the data transmitted from one node to another node in the HMD maybe required to satisfy the real-time data requirement 805. What thismeans is that the ability to re-transmit data, as conventional systemsdo when faced with errors in the data, is now not available for the HMDimplementations. To clarify, re-transmittal to resolve or correct errorsis not available because of the real-time data requirement 805. As such,the disclosed principles introduce a new and different technique forresponding to errors, which technique will be discussed in more detaillater.

The operational requirements 800 also include a low overhead requirement810. As discussed earlier, there is limited bandwidth over the hard linkbetween nodes. The disclosed principles provide techniques for errorcorrection that not only conform to the real-time data requirement 805but that also result in a low amount of additional overhead being placedon the bus protocol. As such, the disclosed embodiments providesubstantial benefits by introducing negligible overhead in order toachieve substantial gains. This negligible overhead is achieved becauseonly certain types of packets (not all) are given error protection,which causes the overhead.

The operational requirements 800 further include a low power requirement815. Based on certain characteristics of the data stream, theembodiments are able to selectively deactivate power-consuming nodes inorder to reduce power. For instance, in the context of an HMD, theembodiments are able to cause lasers to enter a low power state based onthe detection of certain data packets that are transmitted betweennodes.

Some embodiments also conform to a short point-to-point (PTP) interfacerequirement 820 in which the different nodes are positioned a shortdistance relative to one another. As used herein, a so-called “short”distance is one in which transmission loss of the hard link isnegligible as a result of the physical length of the hard link. Examplelengths include, but are not limited to, lengths between 0 inches and upto about 6 inches. Some embodiments also operate at so-called mediumlengths, which are lengths beyond 6 inches and perhaps reaching up to 10inches.

Additionally, the operational requirements 800 include an automatichardware recovery requirement 825 (as opposed to reliance on a softwarerecovery operation). This requirement or feature enables the hardware toautomatically recover after an error is detected. Further discussion oneach of these features will be provided later.

Packets Types

To achieve the above requirements and benefits, some embodiments causespecific types of packets to be transmitted from one node to anothernode in the data stream. FIG. 9 illustrates an example packet 900, whichis representative of the packets that were discussed in FIG. 2 .Notably, packet 900 may take on different forms, including a controldata type packet 905, a non-control data type packet 910, and an endcondition packet 915.

The control data type packet 905 and the non-control data type packet910 are examples of packets that contain data (i.e. data type packets920) while the end condition packet 915 operates as a flag fortriggering a certain action to occur (i.e. a flag informing the receivernode that the data stream is complete). That is, the end conditionpacket 915 gives the status of the virtual lane based on a condition inwhich the control data type packet 905 indicates there was an end forthe data stream, thereby triggering a status bit to be set (per virtualchannel) and thereby triggering the transmission of the end conditionpacket 915.

In some embodiments, after all of the virtual lanes have finishedsending their respective data streams, the last virtual channel tofinish sending its data stream sends an additional final end conditionpacket that gives the status of all of the virtual lanes. Furtherdetails on this feature will be discussed later. In any event, thetransmitter node does not send any new traffic for a virtual channel(e.g., once one or more end condition packets have been transmitted viathat virtual channel) until such time as when all the virtual channelshave completed transmitting their respective data streams for the sweep.When a new sweep is initiated or a new frame is initiated, then thevirtual channels will once again commence sending packets.

As used herein, the control data type packet 905 is a type of packetthat includes control data for controlling how a particular operation isto be performed. For instance, with reference to the HMD example, thecontrol data type packet 905 may include timing information as to when alaser is to emit laser light, payload type information, virtualchannel/lane information, and may further include placement informationas to where (e.g., which specific pixel) the laser is to pulse its laserlight. The control data type packet 905 may also include headerinformation indicating which channel or virtual channel is to be used.For instance, each laser of an HMD may be associated with its ownrespective virtual channel. The control data type packet 905 may includecontrol information and virtual channel information for that virtualchannel's corresponding laser.

In some cases, the content included in the control data type packet 905is compressed (e.g., differentially compressed) and includes data for anentire sweep of the corresponding laser. To clarify, a sweep is anentire line of pixels. The control data type packet 905 may includetiming and placement information not only for a single pixel but ratherfor all of the pixels that are to be illuminated by the onecorresponding laser across the entire line or sweep of pixels. Thecontrol data type packet 905 is the first packet that is transmitted ina data stream across a virtual channel. A different data stream may betransmitted across each one of the different virtual channels, and thecontrol data type packet 905 is the first packet that will betransmitted in that data stream (unless no pixels in a sweep are goingto be illuminated by the corresponding laser, then only an end conditionpacket 915 will be transmitted).

Because of the importance of the control data type packet 905, thispacket is protected using error correcting code ECC 925. To clarify,because the timing and placement information included in the controldata type packet 905 was differentially compressed and of highimportance, ECC 925 is used to protect the data from errors that mayoccur during transmission. If an error were permitted to persist on thedata included in the control data type packet 905, then the entire sweepmay be corrupted, thereby resulting in artifacts (e.g., blurring,jitter, etc.) being introduced into the resulting image frame. FIG. 10provides some additional description regarding ECC 1000, which isrepresentative of the ECC 925 of FIG. 9 .

Specifically, the ECC 1000 includes at least two types of protections,including single bit error correction 1005 and double bit errordetection 1010. In some embodiments, the error protection is an x-biterror correction and an x+1-bit error detection. The ECC 1000 isselected to ensure that the ECC 1000 supports the error rate. The ECC1000 may, in some instances, be 8 bits per control data type packet, orsome other selected number of bits based on the length of the controldata type packet. Selectively imposing the ECC 1000 on the control datatype packet provides substantial benefits, which will be discussedmomentarily.

Returning to FIG. 9 , the non-control data type packet 910 is a packetthat includes payload information, such as for how to illuminate aparticular pixel in a sweep (e.g., color intensity, duration, laserpulse size, etc.). As such, the non-control data type packet 910includes pixel data 930 describing the mechanics of how a pixel is to beilluminated.

Whereas a single control data type packet may be sent in each new datastream across a virtual channel, there may be any number of non-controldata type packets that are sent in the data stream. Furthermore,corruption of any single non-control data type packet may result in onlya single pixel being corrupted. HMDs often have a refresh rate ofbetween 90 Hz and 120 Hz and also have very high resolution rates (e.g.,each image frame is megabytes in resolution quality), so corruption of asingle pixel may not be noticeable by a user of the HMD. In view ofthose conditions, the embodiments selectively refrain from imposing ECCon the non-control data type packet 910. Errors that occur for thenon-control data type packet 910 are simply accepted because theinfluence resulting from any such error is considered nominal.

By imposing ECC 925 on the control data type packet 905, the embodimentssatisfy the real-time data requirement 805 of FIG. 8 because the ECC 925allows for error correction and detection at the receiver node, suchthat a re-transmittal of the control data type packet 905 need not beperformed and real-time processing may be performed. Similarly, byimposing the ECC 925 on only the control data type packet 905 but not onthe non-control data type packet 910 (which typically constitute amajority of the packets transmitted in a data stream), the embodimentssatisfy the low overhead requirement 810 because additional data (i.e.the ECC) is being applied to only a single packet as opposed to multiplepackets. As such, the amount of additional overhead is also nominal.Additionally, by imposing the ECC, the embodiments are able toautomatically recover upon detecting an error (i.e. the ECC enableserrors to be automatically detected and resolved and when a new sweephappens, past errors are not imputed on new sweeps because the endcondition packets informed the receiver node the data stream is completefor that sweep), such that the automatic hardware recovery requirement825 is also satisfied. Accordingly, the embodiments impose differentdata protection requirements based on data type, or rather differentpacket type.

The end condition packet 915 is a packet used to trigger when the datastream is complete. That is, the end condition packet 915 is the lastpacket that is sent over the data stream after all of the non-controldata type packets are transmitted. If no pixels in a particular sweepare to be illuminated by a specific laser, then it may be the case thatno control data type packet or non-control data type packets aretransmitted over that laser's corresponding virtual channel. Instead,only the end condition packet 915 may be sent. In some cases, to helpmitigate against possible errors, a plurality of end condition packetsmay be transmitted. Further discussion on this feature will be providedlater.

Data Streams Across Virtual Channels

FIG. 11 shows an example scenario involving multiple virtual channels1100, which are representative of the virtual channels discussed thusfar and which are transmitting the three different packet typesintroduced in FIG. 10 . FIG. 11 shows a scenario in which there are 12virtual channels, and the data stream flow is flowing from the left tothe right. Additionally, the different packet types are illustratedusing different shading techniques. In this example scenario, eachvirtual channel corresponds to a single respective laser in the HMD, andeach virtual channel has its own corresponding data stream beingtransmitted.

Referring first to channel (ch.) 1, FIG. 11 shows how ch. 1's datastream starts with a control data type packet, then includes fivenon-control data type packets, and then includes an end conditionpacket. Channel 2 is similar in that it includes one control data typepacket, two non-control data type packets, and an end condition packet.Channels 1 and 2 are transmitting data because the lasers correspondingto those channels will be used to illuminate pixels in a sweep. Channel3, on the other hand, corresponds to a laser that will not be used toilluminate pixels in the sweep. As a consequence, the data stream beingtransmitted across ch. 3 includes only an end condition packet. This endcondition packet beneficially informs the receiver node (e.g., theDMA-driving chip 615 from FIG. 6 ) that ch. 3's corresponding laser willnot be used for this particular sweep. Accordingly, if a laser is notgoing to be used during a particular sweep, then the data streamtransmitted for that laser's virtual channel will include only one ormore end condition packets. In this regard, there may be any number ofasynchronous or non-symmetric data flows being transmitted across thedifferent virtual channels. FIG. 12 illustrates some of the benefits ofusing end condition packets.

Specifically, FIG. 12 focuses on virtual channels 1200, which arerepresentative of the virtual channels 1100 of FIG. 11 . For brevitypurposes, only ch. 1 is being displayed, but the ellipsis 1205symbolizes how any number of channels may be present.

FIG. 12 shows how an end condition packet has been transmitted acrossch. 1. It may be the case that the end condition packet followed anynumber of non-control data type packets and a control data type packetor it may be the case that no non-control data type packets and controldata type packet was transmitted. Regardless, the end condition packetoperates as a trigger 1210 to notify that system that a correspondingpower consuming node can be transitioned from a power consuming mode toa reduced power consuming mode. This triggering operation is beneficialbecause the system now knows the power consuming node is idle and thuscan be transitioned to the reduced power consuming mode.

For instance, in the context of an HMD, the HMD includes a laser emitter1215 that itself includes laser 1215A, 1215B, and 1215C. Channel 1 isthe virtual channel corresponding specifically to laser 1215A.Transmitting the end condition packet across ch. 1 causes the system torecognize that use of the laser 1215A is now complete and thus can betransitioned from an active mode 1220 of generating laser light toeither a low power mode 1225 or perhaps even an off mode 1230. The lowpower mode 1225 is a mode in which the laser 1215A consumes less powerthan the active mode 1220 because the laser 1215A is not activelygenerating laser light. The low power mode 1225 may be a mode in whichthe laser 1215A is still turned on, however. The off mode 1230, incontrast, may be a mode in which the laser is entirely turned off. Ofcourse, these principles may be applied to any type of node, and notjust to a laser.

As shown in FIG. 12 , the end condition packet has triggered anoperation in which the laser 1215A is now no longer emitting laserlight, whereas the lasers 1215B and 1215C may still be emitting laserlight. With reference to FIG. 11 , transmitting the end conditionpackets across each of the different virtual channels enables eachvirtual channel's corresponding node to transition to the low powerstate, thereby enabling the system to preserve battery life.Furthermore, transitioning the nodes to the low power state may beperformed asynchronously relative to the other virtual channels. Forinstance, based on the placement of the end condition packets in FIG. 11, the laser (or node) corresponding to ch. 6 will be the first laser totransition power modes. The laser (or node) corresponding to ch. 4 willbe the next laser to transition power modes because its end conditionpacket is next in line relative to the other end condition packets thatare being transmitted.

In some embodiments, multiple end condition packets are transmitted overa virtual channel to mitigate any risks that may occur from errorsduring transmission, which errors may result in any one particular endcondition packet not being recognized as such by the receiving node.Accordingly, FIG. 13 shows a condition in which multiple end conditionpackets 1300 are being transmitted over a virtual channel (i.e. ch. 1).

In FIG. 13 , there are 8 total end condition packets that are beingtransmitted. Sometimes only a single end condition packet is transmittedwhile other times 2, 3, 4, 5, 6, 7, 8, or more than 8 end conditionpackets are transmitted. Either a fixed number of end condition packetsmay always be transmitted or a variable number of end condition packetsmay be transmitted, where the variable number may be based on thestatistical max error rate 1310 that is detected or computed for a datastream transmitted over a virtual channel. Transmitting multiple endcondition packets is often beneficial because transient errors may beintroduced into any single end condition packet, making that packeteither unreadable by the receiver node or undetectable as an endcondition packet by the receiver node. In this regard, redundantlysending multiple end condition packets safeguards against possibleerror-occurring scenarios. Because each end condition packet is beingprovided as a triggering flag, each end condition packet may belightweight and contain only a small amount of information.Consequently, transmitting the end condition packets over the virtualchannel consumes only a negligible amount of bandwidth and resources.

Turning briefly back to FIG. 11 , ch. 1 is shown as being the lastchannel to transmit an end condition packet. Whichever virtual lanetransmits an end condition packet last, then the data stream for thatvirtual lane is tasked with performing a so-called wrap-up operation inwhich its end condition packets constitute a “final” end condition typepacket 1315, as illustrated in FIG. 13 . The final end condition typepacket 1315 provides additional information to the receiver nodeindicating that all the data streams for all the other virtual lanes arealso complete.

Such a feature is beneficial in the context of an HMD because the finalend condition type packet 1315 also symbolizes the end of a sweep. Bysymbolizing the end of a sweep, the display circuitry can effectivelystart anew with the understanding that past errors are now done and anynew errors will be associated with the line of pixels in the new sweep.Additionally, the final end condition type packet 1315 can operate toinform any nodes that were previously transitioned to a low power stateto begin a ramp up process of transitioning back to the active state, ifa ramp up period is needed for those nodes.

FIG. 14 shows a summary view of a data stream 1400 in accordance withthe principles discussed thus far. Data stream 1400 is being transmittedover ch. 1 and includes a control data type packet 1405 as the leadingor first packet, which control data type packet 1405 is protected usingECC 1410. Subsequent to the control data type packet 1405, the datastream includes a non-control data type packet 1415, which is notprotected using ECC. If errors were to occur on the non-control datatype packet 1415, any such errors are allowed and considered acceptablewithout re-transmittal. The ellipsis 1420 indicates how any number ofnon-control data type packets may be transmitted in the data stream1400. After the last non-control data type packet is transmitted, thedata stream 1400 includes one or more end condition packet(s) 1425 thatinform the receiver node the data stream 1400 is complete and thatoperate as a notice that ch. 1's corresponding node can transition to alow power state to thereby preserve battery. Accordingly, theembodiments further satisfy the low power requirement 815 of FIG. 8 byselectively and incrementally transitioning nodes to low power states inresponse to one or more end condition packets being transmitted over avirtual channel.

FIG. 15 shows an example scenario in which the embodiments are able torespond to a hard link error 1500 in which the physical channel betweentwo nodes may become corrupted (e.g., a hard high or low pull), shorted,an input/output I/O issue, a physical chip error, or even physicallybroken. Specifically, FIG. 15 shows two nodes, node 1505 and node 1510,both of which are representative of the nodes discussed thus far. Inthis example, node 1505 is a transmitter node and node 1510 is thereceiver node. In accordance with the principles discussed thus far,node 1505 is sending any number of packets to the node 1510.

Now, however, there is a hard link error 1500 on the channel or virtualchannel. The ellipsis 1515 symbolizes the lack of continued transmittalof packets over a period of time. In some cases, the nodes 1505 and 1510may not be able to directly detect the occurrence of the hard link error1500. As such, the embodiments configure the node 1510 (i.e. thereceiver node) to include a so-called deadman timer 1520. This deadmantimer 1520 may be triggered upon the initial receipt of packets in adata stream. The deadman timer 1520 can continue to elapse time until athreshold amount of time has been reached. This threshold amount of timecan be set to any value but will typically be a value that issubstantially larger than time values usually used to transmit datastreams. For example, the duration of the threshold time period may bebased on past historical trends for data streams. For instance, thethreshold time period may be set to 2×, 3×, 4×, or perhaps even 5× thehistorically identified average period of time in which data streams aretransmitted. From this, one will appreciate how the deadman timer 1520may be used to identify when some error has occurred. That is, if thethreshold period of time used by the deadman timer 1520 elapses afterinitial receipt of a packet, then the node 1510 can determine that theremay be a hard link error 1500.

In some cases, the deadman timer 1520 is triggered when any packet isreceived via any one of the virtual channels or other channels existingbetween the node 1505 and 1510. In some cases, the deadman timer 1520may be triggered in response to some other indication in the system,where the indication indicates that the node 1510 should be receivingpackets but currently is not. Accordingly, the receiver node may includethe deadman timer 1520, which helps the system identify hard link errors1500 and which triggers a timeout for receiving packets from thetransmitter node. In this manner, the hardware is able to automaticallydetect hard link errors.

FIG. 15 also shows an optional retrain 1525 operation. When abus/channel is initially used, it often undergoes an initial training orcalibration operation to identify an “i” (i.e. current) that producesthe lowest possible error rate on the wire for data that is transmittedover the wire. For instance, the calibration is performed to identifydifferences between a “0” bit on the line and a “1” bit on the line. The“i” mentioned above refers to the amount of current above or below athreshold that is needed in order to represent a “1” and how muchcurrent below the threshold is needed in order to represent a “0.” Whenperforming this initial calibration, the system is able to skew ormodify the wire, link, or channel to try to lower the probability oferror by making “i” larger. The larger the “i,” the bigger the currentdifference is required to represent a “1” or a “0.” Performing thiscalibration helps prevent a “0” from being identified as being a “1” andvice-versa on the wire.

In some cases (though perhaps not for cases involving an actual break tothe wire), the embodiments are able to trigger the retrain 1525operation to occur to re-train or re-calibrate the “i” value listedearlier. For instance, if the node 1510 identifies a threshold number ofpackets that have errors, then the node 1510 can trigger the retrain1525 operation. In some specific implementations, the ECC may betriggered to correct a control data type packet, and the triggering ofthe ECC may be further configured to trigger the retraining of the hardlink. As discussed earlier, the ECC (which may trigger the retrainingprocess) can be utilized for errors that are determined to becorrectable based on the design constraints of the ECC. For instance, ifthe ECC is designed to correct single bit errors and detect double biterrors, then single bit errors will be corrected and double bit errorswill be detected. Likewise, if the ECC is designed to correct x-biterrors and detect x+1-bit errors, then x-bit errors will be correctedand x+1-bit errors will be detected. Accordingly, the disclosedprinciples should not be limited to any specific type of ECC or error.

The retain 1525 operation can be scheduled to occur during the vblankperiod that was mentioned earlier. As discussed earlier, the vblank timeoften consumes about 20% of the time scheduled for a frame, so theretrain 1525 operation can be performed during this time period prior tothe illumination of a new frame.

Accordingly, the embodiments are able to use any ECC-corrected errors tooperate as a notice that the hard link may need to be retrained in themanner described above. This retraining process may be performedautomatically (e.g., perhaps by the hardware) during the vblank timeperiod in which the nodes/lasers are typically idle such that no datatransmissions are occurring on the virtual channels.

Example Method(s)

The following discussion now refers to a number of methods and methodacts that may be performed. Although the method acts may be discussed ina certain order or illustrated in a flow chart as occurring in aparticular order, no particular ordering is required unless specificallystated, or required because an act is dependent on another act beingcompleted prior to the act being performed.

Attention will now be directed to FIG. 16 , which illustrates aflowchart of an example method 1600 that may be performed by a computersystem or even any of the HMDs discussed thus far. Method 1600 isconfigured to improve transmissions between a transmitter node and areceiver node via a high-speed high-bandwidth link. These improvementsare achieved by recovering from an error condition without requiring are-transmittal of data across the link. Additionally, the embodimentsare able to isolate a misbehaving or error-prone channels (e.g., aphysical channel or a virtual channel) so that the error-prone channeldoes not impact other channels (virtual or otherwise). Notably, thesystem (e.g., any type of computer system, including an HMD) includesthe transmitter node and the receiver node connected via the hard link.By way of example, the transmitter node may be the DPP chip 610 fromFIG. 6 , and the receiver node may be the DMA-driving chip 615 of theHMD 600. Of course, other types of nodes may be used as well.

Initially, method 1600 includes an act (act 1605) of initiatinggeneration of a data stream that is to include packets of different datatypes, including a control data type and a non-control data type. Forinstance, the data stream 220 from FIG. 2 may be representative of thedata stream in act 1605, and the control data type packet 905 and thenon-control data type packet 910 from FIG. 9 are representative of thepackets discussed in act 1605.

Method 1600 also includes an act (act 1610) of generating a control datatype packet (e.g., the control data type packet 905 from FIG. 9 ) andselectively imposing error correcting code (ECC) (e.g., ECC 925 fromFIG. 9 ) on the control data type packet. This ECC is configured toenable errors occurring in the control data type packet to be correctedat the receiver node. As a consequence, re-transmittal of the controldata type packet is prevented and the hardware is able to automaticallyrecover from the error without a re-transmittal. The ECC on the controldata type packet is configured to perform single bit error correctionand double bit error detection (i.e. SECDED). In some cases, the ECC isdesigned to perform x-bit error correction and x+1-bit error detection,as recited earlier.

Method 1600 also includes an act (act 1615) of causing the transmitternode to transmit the control data type packet to the receiver node. Forinstance, FIG. 11 shows how a control data type packet is transmittedover channel 1. Additionally, each channel or virtual channel may haveits own corresponding data stream. One will appreciate how thetransmission may occur over a virtual channel or a physical channel thatis not virtual. Indeed, the embodiments may be practiced using any typeof channel without limit.

Upon receipt of the control data type packet at the receiver node, anumber of operations may be performed. For instance, act 1620 shows howthe method 1600 includes performing error correction on the control datatype packet using the ECC when an error is detected. Alternatively, act1625 shows how the method 1600 includes refraining from performing errorcorrection when no error is detected. Notably, when ECC is performed,this ECC is performed without impacting data streams that may be flowingacross the other channels or virtual channels. To clarify, by practicingthe disclosed principles, an error on one channel (be it virtual orotherwise) will not impact the operations of the other channels.

In parallel or even in series with acts 1620 or 1625, method 1600 showsan act (act 1630) of generating non-control data type packets (e.g.,non-control data type packet 910 from FIG. 9 ). The non-control datatype packets include pixel data (laser color, color intensity, shape ofthe laser pulse, etc.) used to display content. Act 1630 also includesselectively refraining from imposing the ECC on the non-control datatype packets.

For instance, FIG. 11 shows how ECC is imposed on only the control datatype packets while no ECC is imposed on the non-control data typepackets, which packets typically represent a majority of the packets inthe data stream. The process of selectively refraining from imposing theECC on the non-control data type packets operates to reduce bandwidthusage over the hard link as compared to imposing ECC on the non-controldata type packets. Because there is usually only a single control datatype packet in each data stream, imposing the ECC on that packet willhave only a nominal impact on bandwidth and resource usage.

The transmitter node is then caused (act 1635) to begin transmitting thenon-control data type packets to the receiver node. Upon receipt of thenon-control data type packets at the receiver node and in response tocorruption (i.e. an error) in one or more of the non-control data typepackets being detected, method 1600 includes an act (act 1640) ofallowing the corruption to persist.

Whereas an uncorrected error to the control data type packet may resultin an entire sweep of pixels being corrupted and causing artifacts, anerror to a non-control data type packet often results in corruption ofonly a single pixel of an HMD. A single pixel artifact is often not evennoticeable at the refresh rates used by the HMD. For non-HMDimplementations, corruption of the non-control data type packets mayalso be negligible. The receiver node is able to automatically recoverwhen a single or multibit error is detected in a particular one of thenon-control data type packets by accepting the error for a period oftime (e.g., a time period associated with a sweep) and then resettingerror flags for a new sweep.

Accordingly, by performing the above operations, the embodiments areable to selectively recover from some errors in a data stream (e.g.,errors occurring on the control data type packet) without requiringre-transmittal of the packets. Such operations enable the embodiments tosatisfy real-time requirements for data packets, thereby improving theoperational efficiency of the system while also reducing bandwidth usageof the virtual channels.

FIG. 17 illustrates a flowchart of an example method 1700 that may alsobe performed by any type of computer system, including an HMD. Method1700 is configured to improve power usage by identifying when packettransmissions across virtual channels are complete and by causing nodesto enter a low power state/mode when those packet transmissions arecomplete. The computer system also includes a transmitter node and areceiver node (e.g., any of the nodes discussed thus far) connected viaa hard link. Here, multiple virtual channels are initialized on the hardlink, and each virtual channel is associated with a correspondingpower-consuming node (e.g., perhaps a laser).

Method 1700 initially includes an act (act 1705) of initiatinggeneration of data streams that are to include packets, some of whichinclude different types, including data type packets and end conditiontype packets. For instance, each data stream may include either only endcondition packets or, alternatively, a combination of one control datatype packet, any number of non-control data type packets, and a selectednumber of end condition packets. To clarify, the data type packets mayinclude a control data type packet 905 of FIG. 9 and a non-control datatype packet 910 (or any number of such packets). The end condition typepacket may be the end condition packet 915 of FIG. 9 . As discussedearlier, ECC may be imposed on one or more of the data type packets(e.g., the control data type packets) but is not imposed on any of theend condition type packets.

Method 1700 also includes an act (act 1710) of generating the packetsand causing the transmitter node to transmit the packets to the receivernode over the virtual channels. Each virtual channel transmits its owncorresponding data stream configured in the manner described above suchthat each virtual channel transmits one or more of the different typesof packets.

For each respective virtual channel included in the plurality of virtualchannels, a number of operations are then performed as represented byact 1715. Specifically, act 1715A includes identifying when a final datatype packet has been transmitted across each respective virtual channel.After act 1715A, there is an act 1715B of causing the transmitter nodeto transmit (for each respective virtual channel) one or more endcondition type packets. In some implementations, the one or more endcondition type packets that are transmitted include multiple endcondition type packets. Determining how many end condition type packetsare to be transmitted may be based on different factors, including astatistical max error rate, detected environmental conditions that maycause an increased likelihood of transient errors, and others. In somecases, at least 8 different end condition type packets are transmittedfor each respective virtual channel. In some cases, different numbers ofend condition type packets may be sent for each of the different virtualchannels (e.g., one channel may have 4 end condition type packets sentthrough it while another channel may have 16 end condition type packetssent through it). The redundancy of sending multiple end condition typepackets protects against errors that may occur for any one or more ofthose packets.

Also after act 1715A, there is an act 1715C of causing a correspondingpower-consuming node that corresponds to that respective virtual channelto transition from a powered or active state/mode to a low powerstate/mode. An example will be helpful.

FIG. 11 shows multiple virtual channels, each transmitting its owncorresponding data stream. A data stream may include a combination ofcontrol data type packets, non-control data type packets, and endcondition packets or, alternatively only end condition packets. Inaccordance with act 1715A and with reference to ch. 1, the embodimentsare able to identify when the last non-control data type packet is sent(e.g., in ch. 1 the last non-control data type packet is the fifth fromthe right). In response to that identification step, the embodiments areable to cause the transmitter node to transmit an end condition packet(or perhaps multiple end condition packets). Additionally, as shown inFIG. 12 , the embodiments are able to cause a corresponding node (e.g.,laser 1215A corresponds to ch. 1) to transition from the active mode1220 to a low power mode 1225 or even an off mode 1230.

Returning to FIG. 17 , after the final or last data type packets havebeen transmitted across all of the virtual channels, method 1700includes an act (act 1720) of causing the transmitter node to send afinal end condition type packet to the receiver. The final end conditiontype packet informs the receiver that the data stream is complete notonly for that specific virtual channel but for all of the other virtualchannels as well. The final end condition type packet mentioned in act1720 is representative of the final end condition type packet 1315 ofFIG. 13 . In some cases, the final end condition type packet istransmitted over a particular virtual channel that is last to transmitits non-control data type packets as compared to other ones of thevirtual channels that also transmitted packets.

As discussed above, in some embodiments, the power-consuming nodes thatcorrespond to the plurality of virtual channels are lasers. Furthermore,the final end condition type packet may further inform the receiver nodethat data streams on other ones of the virtual channels in the pluralityof virtual channels are also complete.

Some embodiments are able to perform a combination of the acts recitedin both method 1600 of FIG. 16 and method 1700 of FIG. 17 . None of thedisclosed features are mutually exclusive and any feature recited inthis disclosure may be combined with any other feature, without limit.

Accordingly, the disclosed embodiments operate to improve datatransmissions and also to improve power efficiency. To improve the datatransmissions, the embodiments selectively apply ECC to only a specifictype of packet and refrain from applying the ECC to other types ofpackets. Doing so results in only a nominal increase to resource usageyet results in substantial benefits because now re-transmitting packetsthat have become corrupted can be avoided. The embodiments alsobeneficially transition nodes to low power states upon identifyingconditions in which specific types of packets are detected in a datastream.

Example Computer/Computer Systems

Attention will now be directed to FIG. 18 which illustrates an examplecomputer system 1800 that may include and/or be used to perform any ofthe operations described herein. Computer system 1800 may take variousdifferent forms. For example, computer system 1800 may be embodied as atablet 1800A, a desktop or a laptop 1800B, a wearable device (e.g., HMD1800C, which is representative of the HMDs discussed thus far), a mobiledevice, or any other type of standalone device as represented by theellipsis 1800D. Computer system 1800 may also be a distributed systemthat includes one or more connected computing components/devices thatare in communication with computer system 1800.

In its most basic configuration, computer system 1800 includes variousdifferent components. FIG. 18 shows that computer system 1800 includesone or more processor(s) 1805 (aka a “hardware processing unit”),input/output I/O 1810, display circuitry 1815, and storage 1820.

Regarding the processor(s) 1805, it will be appreciated that thefunctionality described herein can be performed, at least in part, byone or more hardware logic components (e.g., the processor(s) 1805). Forexample, and without limitation, illustrative types of hardware logiccomponents/processors that can be used include Field-Programmable GateArrays (“FPGA”), Program-Specific or Application-Specific IntegratedCircuits (“ASIC”), Program-Specific Standard Products (“ASSP”),System-On-A-Chip Systems (“SOC”), Complex Programmable Logic Devices(“CPLD”), Central Processing Units (“CPU”), Graphical Processing Units(“GPU”), or any other type of programmable hardware.

The I/O 1810 may include any type of input or output device. Examplesinclude, but are not limited to, displays, keyboards, mouse, stylus,joystick, touchscreens, and so forth without limit. The displaycircuitry 1815 is representative of the display circuitry 605 from FIG.6 .

As used herein, the terms “executable module,” “executable component,”“component,” “module,” or “engine” can refer to hardware processingunits or to software objects, routines, or methods that may be executedon computer system 1800. The different components, modules, engines, andservices described herein may be implemented as objects or processorsthat execute on computer system 1800 (e.g. as separate threads).

Storage 1820 may be physical system memory, which may be volatile,non-volatile, or some combination of the two. The term “memory” may alsobe used herein to refer to non-volatile mass storage such as physicalstorage media. If computer system 1800 is distributed, the processing,memory, and/or storage capability may be distributed as well.

Storage 1820 is shown as including executable instructions (i.e. code1825). The executable instructions represent instructions that areexecutable by the processor(s) 1805 of computer system 1800 to performthe disclosed operations, such as those described in the variousmethods.

The disclosed embodiments may comprise or utilize a special-purpose orgeneral-purpose computer including computer hardware, such as, forexample, one or more processors (such as processor(s) 1805) and systemmemory (such as storage 1820), as discussed in greater detail below.Embodiments also include physical and other computer-readable media forcarrying or storing computer-executable instructions and/or datastructures. Such computer-readable media can be any available media thatcan be accessed by a general-purpose or special-purpose computer system.Computer-readable media that store computer-executable instructions inthe form of data are “physical computer storage media” or a “hardwarestorage device.” Computer-readable media that carry computer-executableinstructions are “transmission media.” Thus, by way of example and notlimitation, the current embodiments can comprise at least two distinctlydifferent kinds of computer-readable media: computer storage media andtransmission media.

Computer storage media (aka “hardware storage device”) arecomputer-readable hardware storage devices, such as RAM, ROM, EEPROM,CD-ROM, solid state drives (“SSD”) that are based on RAM, Flash memory,phase-change memory (“PCM”), or other types of memory, or other opticaldisk storage, magnetic disk storage or other magnetic storage devices,or any other medium that can be used to store desired program code meansin the form of computer-executable instructions, data, or datastructures and that can be accessed by a general-purpose orspecial-purpose computer.

Computer system 1800 may also be connected (via a wired or wirelessconnection) to external sensors (e.g., one or more remote cameras) ordevices via a network 1830. For example, computer system 1800 cancommunicate with any number devices or cloud services to obtain orprocess data. In some cases, network 1830 may itself be a cloud network.Furthermore, computer system 1800 may also be connected through one ormore wired or wireless networks to remote/separate computer systems(s)that are configured to perform any of the processing described withregard to computer system 1800.

A “network,” like network 1830, is defined as one or more data linksand/or data switches that enable the transport of electronic databetween computer systems, modules, and/or other electronic devices. Wheninformation is transferred, or provided, over a network (eitherhardwired, wireless, or a combination of hardwired and wireless) to acomputer, the computer properly views the connection as a transmissionmedium. Computer system 1800 will include one or more communicationchannels that are used to communicate with the network 1830.Transmissions media include a network that can be used to carry data ordesired program code means in the form of computer-executableinstructions or in the form of data structures. Further, thesecomputer-executable instructions can be accessed by a general-purpose orspecial-purpose computer. Combinations of the above should also beincluded within the scope of computer-readable media.

Upon reaching various computer system components, program code means inthe form of computer-executable instructions or data structures can betransferred automatically from transmission media to computer storagemedia (or vice versa). For example, computer-executable instructions ordata structures received over a network or data link can be buffered inRAM within a network interface module (e.g., a network interface card or“NIC”) and then eventually transferred to computer system RAM and/or toless volatile computer storage media at a computer system. Thus, itshould be understood that computer storage media can be included incomputer system components that also (or even primarily) utilizetransmission media.

Computer-executable (or computer-interpretable) instructions comprise,for example, instructions that cause a general-purpose computer,special-purpose computer, or special-purpose processing device toperform a certain function or group of functions. Thecomputer-executable instructions may be, for example, binaries,intermediate format instructions such as assembly language, or evensource code. Although the subject matter has been described in languagespecific to structural features and/or methodological acts, it is to beunderstood that the subject matter defined in the appended claims is notnecessarily limited to the described features or acts described above.Rather, the described features and acts are disclosed as example formsof implementing the claims.

Those skilled in the art will appreciate that the embodiments may bepracticed in network computing environments with many types of computersystem configurations, including personal computers, desktop computers,laptop computers, message processors, hand-held devices, multi-processorsystems, microprocessor-based or programmable consumer electronics,network PCs, minicomputers, mainframe computers, mobile telephones,PDAs, pagers, routers, switches, and the like. The embodiments may alsobe practiced in distributed system environments where local and remotecomputer systems that are linked (either by hardwired data links,wireless data links, or by a combination of hardwired and wireless datalinks) through a network each perform tasks (e.g. cloud computing, cloudservices and the like). In a distributed system environment, programmodules may be located in both local and remote memory storage devices.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or characteristics. The described embodimentsare to be considered in all respects only as illustrative and notrestrictive. The scope of the invention is, therefore, indicated by theappended claims rather than by the foregoing description. All changeswhich come within the meaning and range of equivalency of the claims areto be embraced within their scope.

What is claimed is:
 1. A method for recovering from an error conditionwithout requiring a re-transmittal of data across a link, said methodcomprising: causing a data stream to include packets of different datatypes, including a control data type and a non-control data type;generating a control data type packet and selectively imposing errorcorrecting code (ECC) on the control data type packet, the ECC enablingerrors that occur in the control data type packet to be correctedwithout re-transmittal of the control data type packet; transmitting thecontrol data type packet in the data stream; generating a non-controldata type packet and selectively refraining from imposing the ECC on thenon-control data type packet; and transmitting the non-control data typepacket in the data stream.
 2. The method of claim 1, wherein the ECC onthe control data type packet performs one of: single bit errorcorrection or double bit error detection.
 3. The method of claim 1,wherein a length of data included in any particular packet of the datastream is restricted based on a buffer size of a virtual channel.
 4. Themethod of claim 1, wherein the ECC is 8 bits per control data typepacket.
 5. The method of claim 1, wherein the non-control data typepacket is one of a plurality of non-control data type packets, andwherein the plurality of non-control data type packets constitute amajority of packets transmitted in the data stream.
 6. The method ofclaim 1, wherein a deadman timer triggers a timeout for receivingpackets.
 7. The method of claim 1, wherein an automatic recovery occurswhen a multibit error is detected in the non-control data type packet.8. The method of claim 1, wherein the ECC is further configured totrigger retraining of the link.
 9. The method of claim 1, wherein abandwidth used by the link is more than 4 times a bandwidth used byPCIe.
 10. The method of claim 1, wherein the non-control data typepacket includes pixel data used to display content.
 11. A computersystem that facilitates recovery from an error condition withoutrequiring a re-transmittal of data across a link, said computer systemcomprising: at least one processor; and at least one hardware storagedevice that stores instructions that are executable by the at least oneprocessor to cause the computer system to: cause a data stream toinclude packets of different data types, including a control data typeand a non-control data type; generate a control data type packet andselectively impose error correcting code (ECC) on the control data typepacket, the ECC enabling errors that occur in the control data typepacket to be corrected without re-transmittal of the control data typepacket; transmit the control data type packet in the data stream;generate a non-control data type packet and selectively refrain fromimposing the ECC on the non-control data type packet; and transmit thenon-control data type packet in the data stream.
 12. The computer systemof claim 11, wherein the ECC on the control data type packet performssingle bit error correction.
 13. The computer system of claim 11,wherein the ECC on the control data type packet performs double biterror detection.
 14. The computer system of claim 11, wherein a lengthof data included in any particular packet of the data stream isrestricted based on a buffer size of a virtual channel initialized forthe link.
 15. The computer system of claim 11, wherein the non-controldata type packet includes pixel data used to display content.
 16. Amethod for facilitating power usage by identifying when packettransmissions across virtual channels are complete and by causing nodesto enter a low power mode when those packet transmissions are complete,said method comprising: causing data streams to include packets, some ofwhich are of different types, including a data type and an end conditiontype; generating the packets and transmitting the packets over aplurality of virtual channels; for at least one virtual channel includedin the plurality of virtual channels, performing the following:identifying when a final data type packet has been transmitted acrosssaid at least one virtual channel; transmitting, for said at least onevirtual channel, one or more end condition type packets; and causing acorresponding power-consuming node that corresponds to said at least onevirtual channel to transition from a first mode to a second mode. 17.The method of claim 16, wherein the power-consuming nodes are lasers.18. The method of claim 16, wherein error correcting code (ECC) isimposed on a control data type packet included among the data typepackets but is not imposed on any of the end condition type packets. 19.The method of claim 16, wherein the one or more end condition typepackets that are transmitted include multiple end condition typepackets.
 20. The method of claim 19, wherein determining how many endcondition type packets are to be transmitted is based on a statisticalmax error rate.